This disclosure relates generally to drive-by-wire steering systems. More specifically, this disclosure relates to drive-by-wire steering systems having a steering wheel return mechanism.
Vehicles require a steering system to control the direction of travel. Previously, mechanical steering systems have been used. Mechanical steering systems typically include a mechanical linkage or a mechanical connection between the steering wheel and the vehicle""s road wheels. Thus, movement of the steering wheel causes a corresponding movement of the road wheels. Movement of such mechanical systems is often power assisted through the use of hydraulic assists or electric motors.
Mechanical steering systems are being replaced and/or supplemented by electrically driven steering systems, commonly known as xe2x80x9csteer-by-wirexe2x80x9d systems. Such steer-by-wire systems to varying extents replace, for example, the mechanical linkage between the steering wheel and the vehicle wheels with an electrically assisted system.
This migration to steer-by-wire systems is being made to improve fuel economy, increase vehicle modularity, reduce load on the engine of the vehicle, reduce vehicle weight, and provide four-wheel-steering. For example, the use of steer-by-wire systems eliminates the need for hydraulic fluids, provides a tighter turning radius, and reduces the weight of the vehicle.
Additionally, steer-by-wire systems eliminate various undesirable problems present in mechanical systems. For example in steer-by-wire systems, the steering wheel is mechanically isolated from the road wheels. Thus, excessive deleterious feed back to the steering wheel in the form of shudders, and steering wheel kickback from the road wheels is eliminated.
Unfortunately, mechanically isolating the steering wheel from the road wheel also eliminates desired feed back. For example, during the use of mechanical steering systems, an operator applies a force to the steering wheel to turn the road wheels of the vehicle. After releasing the turning force on the steering wheel, the gyroscopic and other forces on the road wheels tend to act on the mechanical steering system to return the steering wheel to its normal or center position. Unfortunately, the mechanical isolation provided by drive-by-wire steering systems eliminates this desired feedback. Namely, during the use of drive-by-wire steering systems, the steering wheel maintains its turned position after being released instead or returning to its center position.
In vehicles having mechanical steering systems, the force applied by the operator to the steering wheel to turn the road wheels of the vehicle is typically proportion to the amount or degree of vehicle turn desired. Namely, in order to turn the vehicle slightly, only a slight force must be applied to the steering wheel. Conversely, in order to turn the vehicle sharply, a large force must be applied. It is known to provide mechanical steering systems with power assistance through the use of hydraulic assists or electric motors to reduce the amount of force applied to the steering wheel necessary to turn the road wheels. Thus, it has been seen that xe2x80x9cover assistingxe2x80x9d by removing all of the force associated with turning the vehicle, or even making the force required to turn the vehicle constant regardless of the degree of turn changes the xe2x80x9cfeelxe2x80x9d of the steering system.
In mechanical systems, the amount of assistance applied by the hydraulic assists or electric motors has been regulated so as to avoid these xe2x80x9cover assistxe2x80x9d problems. However, during the use of drive-by-wire steering systems the force applied to the steering wheel necessary to turn the wheels is both minimal and constant due to the mechanical isolation of the steering wheel from the road wheels. Thus, prior drive-by-wire steering systems often suffer from the same problems experienced in overly assisted mechanical steering systems.
A drive-by wire steering system comprising a steering shaft and a steering wheel return mechanism is provided. The steering shaft is configured for a first angular displacement about a first axis. The steering shaft comprises a first geared portion and a first end, where the first end is connectable to a vehicle""s steering wheel. The steering wheel return mechanism comprises a torsion member and a second geared portion. The first geared portion and the second geared portion are operatively engaged such that the first angular displacement of the steering shaft imparts a second angular displacement about a second axis to the steering wheel return mechanism. The torsion member is configured to generate a returning torque on the steering wheel return mechanism upon the second angular displacement of the steering wheel return mechanism. The returning torque has a direction opposite the first angular displacement, and is proportional to the second angular displacement.
A method of returning a steering shaft in a drive-by wire steering system to a center position is provided. The method comprises engaging a steering wheel return mechanism to the steering shaft and connecting a torsion member to the steering wheel return mechanism. The steering wheel return mechanism is engaged to a steering shaft such that an angular displacement of the steering shaft about a first axis imparts a second angular displacement about a second axis to the steering wheel return mechanism. The steering shaft is connectable to the vehicle""s steering wheel. The torsion member is connected to the steering wheel return mechanism such that the torsion member generates a returning torque on the steering wheel return mechanism when subjected to the second angular displacement. The returning torque acts on the steering wheel return mechanism to return and maintain the steering wheel at the center position.
A method of improving the stability of a vehicle having a drive-by wire steering system is provided. The method includes calculating a maximum desirable angular displacement of a steering wheel from vehicle conditions, comparing an actual angular displacement of the steering wheel to the maximum desirable angular displacement, and activating an over-rotation device if the actual angular displacement is greater than or equal to the maximum desirable angular displacement. The vehicle conditions include sensed inputs and constant inputs. Upon activation of the over-rotation, the steering wheel is not displaceable past the maximum desirable angular displacement.
The above-described and other features are appreciated and understood by those skilled in the art from the following detailed description, drawings, and appended claims.